Just went back through my u/s reports to check my SD ratio to see if it helps you.

22w: 5.3
25w: 3.6
27w: 5.7
28w: 4.4
29w: 5.9
31w: 4.7
32w: 5.2
33w: 6.9
And DD was born shortly after.

ETA: I had oligohydramnios, too. When you say your fluid is 3.2cm, is that the Index or Deepest Pool?